Owing to high brightness, fast response speed, light weight, thin and small features, full color, no viewing angle differences, no need for an LCD back-light board and low electrical consumption, an organic light emitting diode display or organic electroluminescence display (OLED) takes the lead to substitute a twist nematic (TN) or a super twist nematic (STN) liquid crystal display. Further, it substitutes for a small-sized thin-film transistor (TFT) LCD to become a new display material of fabricating portable information products, cell phones, personal digital assistant (PDA) and notebook.
The organic light emitting diode display comprises passive matrix organic light emitting diode displays (PMOLED) and active matrix organic light emitting diode displays (AMOLED). Thin film transistors in combination with signals of a storage capacitor are used in the AMOLED to control the gray scale presentation of the organic light emitting diode. After the scan line sweeps, the original brightness of the pixels is still maintained. However, for the PMOLEDs, only the pixels selected by the scan line will be lighted. Hence, it is not necessary to drive the organic light emitting diodes in the AMOLED to the very high brightness, and the AMOLED has a long lifetime and a high resolution.
Please refer to FIG. 1, which is a schematic side view of a structure of the AMOLED. The thin film transistor 1 of the AMOLED includes a gate metal 11, a dielectric insulation layer 12, a source/drain metal 13, an amorphous silicon layer 14, a doped amorphous silicon 15 and a passivation layer 16. The organic light emitting diode 2 of the AMOLED includes an indium tin oxide (ITO) electrode 21, an organic emitting layer 22 and a cathode electrode 23. The ITO electrode 21 is connected to the source/drain metal 13. Since the AMOLED is a current-driven element, a given current has to be provided to maintain the consistent brightness of the organic light emitting diodes.
As shown in FIG. 1, the current passes the source/drain metal 13 of the TFT 1 through the ITO electrode 21 and flows into the organic emitting layer 22 and the cathode electrode 23, as shown in the direction of the arrows, and then the organic light emitting diode radiate light. However, in the current technology, the brightness of the organic light emitting diode decays when the given current is provided. Therefore, it is desired to find out the causes of the unstable brightness of the AMOLED and to improve the structure of the AMOLED so as to fabricate an AMOLED capable of maintaining the brightness of the organic light emitting diode.